I think nachos (typically with the fake liquified nacho "cheez"), cheese fries (with the same "cheez" as the nachos, or onion rings are snack bar mainstays. Hot dogs, hamburgers, ice cream novelties, also. A lot of snack bars I've seen have had some low quality "frozen" style pizza. If you're in new england, you'll have some fried seafood on the menu of every snack bar. If you're in the south, I imagine most snack bars have some form of bbq.